I'm trying to grasp whether and when a protein rest would be beneficial for certain grists. I've seen a few rules of thumb thrown around related to the Kolbach index and the total protein percentage. I've generally heard that a protein rest may be beneficial when the Kolbach index is lower than 38%. Likewise, I've heard that a protein rest should probably be done for grists with a weighted average total protein percentage of 12 or greater.

First, are these rules of thumb accurately stated? If so, are they worth following?

Second, what if I have a grist for which the Kolbach index is 35 but the total protein percentage is 10. Would a protein rest be beneficial? I guess what I'm really asking is how do these numbers relate to each other when trying to determine whether or not to do a protein rest.

I've always used the 12%+ ROT for protein rests. I'm happy with the results generally.

I think it's good to think of the protein % and Kolbach as a sort of sliding scale. A lot of pro breweries use very short protein rests, like 5min in some cases. If you're just barely out of the "ideal" range, maybe a very short protein rest would beneficial. I can't say I've done many mashes that were low in total protein and also undermodified, so maybe someone else can comment on that scenario. I seem to remember Noonan talking about ancillary benefits from protein rests, but maybe I'm wrong, and I don't have his book in front of me.

You have to try these days to get SNR < 38, but that's probably a fine rule of thumb.

I typically only do one more around the 12% rule of thumb so unless you are buying crap malted barley (or six row, but typically you are mating that with a nitrogen diluting adjunct) basically wheat beers.

I like to dough in "cold" (104 F) for a number of reasons. Cheap insurance against getting a random bag of undermodified malt from the corner of the malting bin or something (so I get some beta glucan degredation), I don't have to stir (no gelatinization = no dough balls), and I have time to fix the pH if needed before I get to the important rest. So in heating to my next rest (145 typically at 2 degrees F per minute) I guess I get some proteolysis, but no ill effects noted.

Then there was that interview on TBN last year with Dr. Bamforth where he dropped the bombshell that far more proteolysis inhibiting enzymes survive malting than proteolytic enzymes and proteolysis doesn't really happen in the mash anyway. So I don't know what to think. I've been meaning to look into that but I get lazy around technical journals since I don't hang out at libraries or have an ASBC membership. Also as I get older I am less interested in technical reading and my background is not in natural sciences anyway. If someone has any insight on this issue and can explain it to me like I'm 15, I would love to hear it.

Johnf - I remember that interview, now that you mention it. I trust pretty much everything Bamforth says about brewing.

I was wrong about the protein rest. I double-checked New Brewing Lager and Noonan says to never use a stepped mash with British or Brewer's malts, because the low-temp rests would effectively "over-modify" the malt.

For lager malts, Noonan gives 30-33% SNR is undermodified, 37-40% is overmodified. For ale malt 38-42% is the sweet spot, while 50% is too much. He does say if the malt is over the recommended range, brewers should shorten the length of steps, or increase the temp of steps. If the malt is under the desired range, you should lower the sacc. rest length or temperature, and add or lengthen a protein rest.

In some of the commercial recipes I've seen, I've noticed higher-than-usual sacc. temps, like 160-162* so maybe this is why.

To get back to PawPat's original question, maybe we should think about what the Kolbach is measuring. Total nitrogen affects yield, clarity, and head retention. 30-40% of nitrogen in malt will become "permanently soluble" during the mash and I assume the rest will precipitate out during the boil and chill. Half of the soluble nitrogen is formed during malting, the other half during proteolysis during mashing. At 50%+ SNR the beer will lack body, and over 12% total protein the beer may cause haze problems.

So in PawPat's example, I would guess it's more likely that the low SNR will be a bigger problem than a low total amount of protein, but I'm still thinking about this and may come up with more later.

Thanks for the great responses. This is turning into an interesting discussion. Unfortunately, I only have access to the forum on my phone while I'm at work and don't feel like using my thumbs to respond to everything. I'll try to reply tonight when I get home.

Where I was going with the word problem I was working through (and correct me if I make any mistakes) is that if half of the potentially soluble protein is latent in the malt, then that means that another half of the total potential soluble protein 'could' be made soluble through proteolysis (if that's actually possible, per Bamforth).

If you're starting out with 35% SN you could theoretically end up with 70% SN given a long enough protein rest. But you'd never want to have that much soluble nitrogen anyway. Since the total protein percentage is derived from the total nitrogen content (nitrogen x 6.25 = protein), I wonder if the "12% percent protein do a p-rest" ROT is derived from the relationship with the SNR.

But wouldn't insoluble nitrogen precipitate out and not be present in the finished beer? Noonan also says it's the albumin (water-soluble proteins) that gives beer body and head retention, not protein, so I'm not sure why having an SNR over 50% would cause thin mouthfeel.

When you do a protein rest, it breaks down big proteins into soluble proteins, but the total amount of nitrogen won't change, only the ratio of soluble/insoluble will change, potentially to over 50% soluble which would be "bad." So the 12% ROT doesn't make any sense to me, now that I think about it.

"The goal of malting and mashing is not the complete conversion of the malt's protein content, but the creation of a balanced mix of short (amino acids) and medium chained proteins. These become water soluble and, because they don't coagulate during the boil, will be carried over into the cast-out wort (the wort that is later fermented to beer). Amino acids are a necessary yeast nutrient and low FAN (free amino nitrogen) levels can lead to sluggish and unhealthy fermentations. Medium chained proteins are important for the perception of body in the beer as well as the foam stability.

In contrast to the starch conversion there is no simple set of enzymes or substrate that needs to be converted. Generally, when a protein rest is held in a mash, it is held between 122ºF (50ºC) and 133ºF (55ºC) where protoelytic activity shows a maximum. But even at higher temperatures, and in the starch conversion range is significant protein conversion happening [Narziss, 2005].Rest temperatures closer to 122ºF (50ºC) tend to produce more short chained proteins (amino acids) while depleting the long and medium chained proteins. In sufficiently modified malts, this depletion of medium chained proteins can lead to a loss of body and head retention.

Rest temperatures closer to 155ºF (55ºC) emphasize the formation of medium chained proteins. Such a rest is better suited for most modern European lager malts. A dough at this temperature also benefits the fermentability if the mash lacks enzymatic strength.

Overmodified malts (like English or American Pale malts) do not require a protein rest. Since the protein conversion has been driven to a fairly advanced point during the malting process a protein rest may actually hurt by depleting the head and body positive medium chained proteins. For such malts a dough-in above the protein rest range or a simple single infusion mash is best."

According to Palmer, "Modification is the term that describes the degree of breakdown during malting of the protein-starch matrix (endosperm) that comprises the bulk of the seed." Based on this definition, it would seem that the most important number for determining whether to do a protein rest is the SNR (aka Kolbach index). In other words, if the SNR is in the "sweet spot" for a particular malt, i.e., the malt is well-modified, then the brewer need not be too concerned about a high total protein % because the protein-starch matrix will break down fairly easily at saccharification temps.

For example, Weyermann dark wheat malt has an average SNR of 42.75% and a total protein average of 12.25% (according to data pulled from the company's website). 42.75 is obviously a high degree of modification, which, as I understand things, should allow for fairly easy degradation of the 12.25% protein. Therefore, I would conclude that a protein rest is not necessary. If the malt were only moderately or under-modified (e.g., SNR of 35), I would conclude that a protein rest would be beneficial.

PawPat - I think you're right that Kolbach is the most important thing. I doublechecked the wheat malt I use. It's 15% protein and S/T is 34%. I use a protein rest when using a large amount of this malt, with good results. I suspect the protein rest works because of the low Kolbach and not because it has high protein.

I found an analysis for Briess wheat malt and they gave P=12% and S/T=44%, so it looks like my wheat malt is less modified than some.

PawPat - I think you're right that Kolbach is the most important thing. I doublechecked the wheat malt I use. It's 15% protein and S/T is 34%. I use a protein rest when using a large amount of this malt, with good results. I suspect the protein rest works because of the low Kolbach and not because it has high protein.

I found an analysis for Briess wheat malt and they gave P=12% and S/T=44%, so it looks like my wheat malt is less modified than some.

It's from the Colorado Malting Company. They have a really small distribution and they're a newer maltster, so I think they're still learning. The wheat they use is really good stuff (very aromatic and tasty) but their malt is a bit undermodified compared to the big boys.

I just bought a bag of Simpsons Golden Promise and was surprised by the malt analysis for it. Total protein is 8.8% and Kolbach index is 50. I think that's the most modified malt I've ever seen. Looks like a good candidate for single infusion, high temp mashes.

I just bought a bag of Simpsons Golden Promise and was surprised by the malt analysis for it. Total protein is 8.8% and Kolbach index is 50. I think that's the most modified malt I've ever seen. Looks like a good candidate for single infusion, high temp mashes.

I've used that malt a lot and it performs really well in single infusion mashes. Great clarity, great flavor. It's really nice in bitters that you might want to have a sweeter maltiness than with Maris Otter.